Abstract
Radio astronomy in the Netherlands began with a simple comment, almost an afterthought, posited by Jan Oort to his protégé Henk van de Hulst: radio astronomy could become important if there were at least one line in the radio spectrum. The contours of the rest of the story are fairly well known. Van de Hulst suggested several line possibilities (recombination lines) and particularly noted the fine structure transition of atomic hydrogen (with an energy difference corresponding to a wavelength of 21 cm). His results were presented at a small gathering of Dutch astronomers at the Leiden Observatory in April 1944; 7 years later 21 cm radiation from space was detected, at Harvard by Ewen and Purcell, and 6 weeks later by Muller and Oort at Kootwijk, the Netherlands.
This part of the story occupies just a handful of pages in Elbers’ fine, diligently researched history. Most of the book is devoted to what came after the HI prediction and discovery: the construction of the Dwingeloo 25 m antenna, the design of a much larger cross-type radio telescope (the Benelux Cross – BCAP) and how that came to nothing, and the project’s transformation into the Westerbork Synthesis Radio Telescope (WSRT). It is well known that Dutch astronomers had little access to the technical know-how needed to fashion a radio telescope, so they had to find appropriate partners. Oort, who (as is noted several times) usually approached the very top, had soon after the war contacted Martin Ryle. Despite a congenial relationship with him (both were keen sailors), Oort was unable to arrange for a member of the Cambridge group to spend time in the Netherlands – Ryle couldn’t spare anyone. (By the second half of the 1950s, he did get a recent Cambridge PhD recipient, Robin Conway, who would a decade later be my supervisor at Jodrell Bank, to spend a year in Leiden as a post-doctoral fellow.)
The search continued (“Looking for partners,” as the book puts it, p. 31), by 1951 having interested the prominent Belgian astronomer Polydore Swings (p. 120) to join the board of the newly created Foundation for Radio Astronomy. Swings seldom attended meetings, however, and after 4 years a parting of the ways was mutually agreed upon, although by 1960 Belgium did become involved in the BCAP. The book describes how the missing technical expertise was overcome, first by recruiting two recently graduated Dutch radio engineers (Lex Muller and Ben Hooghoudt), and then by attracting young astronomers who had earned their stripes elsewhere: Charles Seeger (from the United States) and Jan Högbom (a Swede who had gained his PhD in Ryle’s group). In the longer term, other foreign experts joined the effort, while Dutch students acquired radio astronomy skills through their university training. Of the latter, few make it into the pages of this book; besides Seeger and Högbom, only the radio astronomers Chris Christiansen and Bill Erickson get as much as a modest mention.
The roles which these “secondary” players assumed are clear enough. Hooghoudt took on the design of the antennas, Muller specialized in receivers for amplifying and recording the extremely weak sky radio signals (both men were involved almost from the start with the Dwingeloo 25 m dish and 15 years later they saw the WSRT get off the launch pad). Of the others, Seeger and Erickson were involved in the BCAP effort before returning to the United States, while Christiansen and Högbom took part in the BCAP and its metamorphosis to become the WSRT.
True to the book’s subtitle, “the politics” of Dutch radio astronomy is extensively investigated. “The people” are also covered, but as just suggested, the coverage is selective and heavily weighted towards “key” figures (like Marcel Minnaert, Henk van de Hulst, and especially Jan Oort). This is understandable, but in some respects a pity. Oort himself was much aware of his own limitations with regard to the technical aspects of radio antennas and receiver systems (he was happy to leave such matters to the engineers, as he once told me). Antennas, feed systems, and receivers, all clearly essential to the operation of a radio telescope, are barely mentioned in Elbers’s book.
The Rise of Radio Astronomy in the Netherlands is not a book about the nitty-gritty of radio technique. Computers (and their software) are also an essential part of a modern radio telescope, especially one which produces images by measuring interferometer visibilities (p. 192). While computing and software are occasionally mentioned with regard to the WSRT, this refers to the role of the Philips electronics firm in providing soft- and hardware for steering the 25 m dishes and reading out the data (p. 205). A serious oversight is that no mention is made of the significant software effort undertaken by Wim Brouw and colleagues. Despite the book’s shortcomings enumerated above (and my criticisms elaborated in JAHH, 21/1 (2018), 95–96), Elbers’ text should be essential reading for anyone interested in the birth of radio astronomical research in the Netherlands.